Conventionally, an EGR apparatus is known, in which the exhaust gas of an internal combustion engine is introduced as the EGR gas into an intake system of the internal combustion engine. When the EGR gas is supplied to the internal combustion engine, it is possible to contemplate the reduction of NOx contained in the exhaust gas and the improvement in the mileage or fuel efficiency. In recent years, in order to further enhance the effect brought about by the supply of the EGR gas, a technique has been developed to further increase the supply amount of the EGR gas, for example, by increasing the diameter of the EGR passage.
In the case of the internal combustion engine provided with the EGR apparatus, if the failure or malfunction, in which the EGR valve provided for the EGR passage sticks or remains in a valve open state (hereinafter referred to as “stuck open”), arises, the EGR gas amount is excessively increased in some cases. If the EGR gas amount is excessively increased, it is feared to cause the accidental fire, the torque fluctuation, and the increase in the discharge amount of the unburned fuel component. Further, if it is contemplated to increase the EGR gas amount as described above, the problem as described above tends to arise more easily.
Patent Document 1 discloses a technique in which the valve operation is stopped in relation to some cylinders to perform the operation with a decreased number of cylinders when an EGR valve is stuck open in an internal combustion engine provided with an EGR apparatus. When the operation is performed with the decreased number of cylinders, it is possible to increase the intake air amount per one cylinder. As a result, it is possible to lower the EGR ratio.